Proximity sensors have been heretofore known and utilized, and such sensors have heretofore included a resonant circuit having an amplitude that varies in accordance with the distance between a conductive object and a probe sensor that is one element of the resonant circuit. A detector has also been heretofore utilized with such devices to provide an output that is based upon the detected amplitude and hence is indicative of distance.
Feedback oscillators of the Hartley or Colpitts types have been heretofore known in which the inductive coil of the LC resonant circuit have been utilized as the sensing element in a probe, but such oscillators have not proved to be completely satisfactory.
In addition, a linear oscillator for a proximity device has also been heretofore suggested (see U.S. Pat. No. 4,001,718). In this device, however, a power source is utilized that requires one of the power components (either voltage or current) to be fixed.